The unit implement a complete data exchange of a Modbus master communication line. The main features are:

• Usable with serial communication line (master) or with TCP/IP protocol (client).
• Communication with several slaves (maximum 32) that can have inhomogeneous communication parameters.
• Management of a process table to read and write data continuously.
• Management of a parameter table with the possibility to perform complete read or write to or from a slave.
• Internal state machine to clearly identify the operating status of the unit.
• Message counters (processed successfully and error message).

The large circles represent stable states. They are:

STOPPED: state where the unit does not perform any activity. It is also the initial state.

READY: state of full activity

ABORT: there is a serious error, the unit switches to the safe state and waits for a stop command. AbortCode provides an identification code of the reason that set that state.

The rectangles indicate transient states:

STARTING: state in which the unit checks all the settings data and if the values are within the limits opens the communication channel.

STOPPING: nothing do in this implementation.

ABORTING: nothing do in this implementation.

Baloons are commands that can be sent to change the state:

Prepare, commands the unit to switch into ready state. Prior to this command must be configured all the communication parameters.

Stop, commands the unit to switch into STOPPED state. The communication channel is closed if it was open.

The unit operation is represented by the following blocks:

The following table shows the Modbus standard functions that are available.

* These functions are currently selectable, but not yet fully developed.

It's a table that contains the communication parameters for each slave. You can enter the parameters for up to 32 slaves.

Using TCPIP protocol:

SlaveId : It's the real ID of the Modbus protocol set in the slave.
SlaveBitrate : It's the baud rate (we support all values compatible with the device MODBUS).
SlaveStopBits : It's the stop bit (0,1,2).
SlaveParity : It's the parity (0 = NONE, 1 = ODD, 2 = EVEN).
SlaveTimeout : It's the maximum value of waiting for a response before reporting a timeout error.
SlaveAddrOffset : It's a value that is added to the address before sending the Modbus message. It's used for matching the numbering of the address used in the tables of this unit with the values shown in the documentation of the slave.
SlaveTcpAddr3 : It's the tcpip address position 3 [Highest] ⇒ 3.2.1.0
SlaveTcpAddr2 : It's the tcpip address position 2.
SlaveTcpAddr1 : It's the tcpip address position 1.
SlaveTcpAddr0 : It's the tcpip address position 0 [Lowest].
SlaveTcpChangeIpDly : It's a waiting time in milliseconds used at every tcpip address change [min. 1, default 500].

It's a configuration table for a communication of data process. The process values are stored on an array (called ProcessValue) where each data element is located at a certain index value. The calculation of the index value for each data is done automatically by the unit based on the data of ProcessTable. The communication of process data can be enabled or disabled with the parameter ProcessEnable.
In order to optimize the occupation of the Modbus® channel, communication process can using multiple messages. Also you can place in ProcessTable write command messages.
An example of the communication process can be a reading of the statusword inverter, writing of the motor speed, reading of the torque value of the motor, reading the temperature value by a temperature controller, etc..
The ProcessTable has a size of 100 rows that must be used for the process data exchange of all slaves; the array ProcessValue has a size of 300 elements. When the unit encounters a line with ProcessId equal to zero, it resumes scanning from start (row 1). To suspend the communication of a specific row simply set ProcessId to a negative value.

ProcessTable

ProcessValue

ProcessId : It's the slave index that indicates that you want to communicate with the slave whose parameters are represented by the row indicated by the value in SlaveTable.
ProcessAddr : It's the Modbus address.
ProcessNum : It's the number of elements (for multiple reading or writing).
ProcessType : It's the Modbus function type.
ProcessOffset : It's the ProcessValue array index where the values will start to be stored. This value is calculated automatically when you start the unit.
ProcessDevErr : It's the err parameter value of the device in the case of error communication.

It manages communication used to perform operations on slave configuration registers (call parameters). This table includes all the information needed to identify these parameters. It 'a single table for all slaves. This table can be included only the data manipulated by the message Modbus® 3 (read holding register) or 6 (force holding register). Are not possible communications using coils, inputs, inputs registers and multiple operations.

The size established for this table is to hold a maximum of 200 parameters.
To enable communication with the Param data type you must use the LowMailBox described below.

ParamId : It's the slave index that indicates that you want to communicate with the slave whose parameters are represented by the line indicated by the value in SlaveTable.
ParamAddr : It's the Modbus address.
ParamNum : Normally set to 1, the value is set 2 to treat certain 32bit data which are composed of two words Modbus®.
ParamOptions : You can specify some details about communication (shown below).
ParamValue : It's the read value or the value to be written.

ParamOptions
The ParamOptions is used to set certain communication characteristics. It runs with the following bit masks:

It's a technique of traffic light system for communication between the various units. This unit includes two Mailbox, the HighMbox and LowMbox. This character allows to various units of the Qview project to share with simplicity the Modbus® communication.
Here's an example:

Both HighMbox and LowMbox are an array of 38 elements, that will be explained subsequently.

In HighMbox[1] and LowMbox[1], there are states and commands to mailboxes:

The variable LowMboxProgress is updated during LowMbox commands and takes values from 0 to 100 to indicate the progress of the operation. It can be used in hmi to manage a progressbar.

We see a sample code for any unit that wants to perform a read:

WAIT MDBMAST1.HighMbox[1] EQ MDBMAST1.MBOX_FREE        ; wait for empty mailbox
MDBMAST1.HighMbox[2] = 1                               ; first slave in configuration table
MDBMAST1.HighMbox[3] = 100                             ; address
MDBMAST1.HighMbox[4] = MDBMAST1.READINREG              ; type
MDBMAST1.HighMbox[5] = 5                               ; num
MDBMAST1.HighMbox[6] = 0                               ; tout (use default)
MDBMAST1.HighMbox[1] = MDBMAST1.MBOX_SINGLE_REQUEST    ; start request
WAIT MDBMAST1.HighMbox[1] EQ MDBMAST1.MBOX_REPLY       ; wait for reply
IF MDBMAST1.HighMbox[6] EQ 0                           ; successfully ?
    Myvar = MDBMAST1.HighMbox[7]
ENDIF
MDBMAST1.HighMbox[1] = MDBMAST1.MBOX_FREE              ; mailbox is now free for other units

We can do the same function with LowMbox (the difference between High and Low will be explained subsequently).

The function checks the parameters of a slave if they coincide with the values contained in ParamValue.

The function checks the parameters of all slaves if they coincide with the values contained in ParamValue.

The function reads the parameters of a slave and stores them in ParamValue.

The function writes the parameters of a slave with the values stored in ParamValue.

The difference between HighMbox and LowMbox consists in the fact that the HighMbox has the possibility of entering during a multiple request commanded on LowMbox, in order to have always the possibility of swift action on variables of high priority.

Let's see how the priority of requests are menaged. Denote by:
P = request regarding the ProcessTable
H = request regarding the HighMbox
L = request regarding the LowMbox

1. With process active, it is required a high priority reading:
   
   The request is immediately inserted between each ProcessData request.
   
   
2. The LowMbox requests are inserted alternating with the ProcessData so the unit meets alternately one row of the ProcessTable and a row of the ParamTable (in the example it is assumed that the LowMbox requests an operation of read parameters of a slave, via the command LowMbox [1] = MBOX_PARAM_READ):
   
   
   
3. In the last example with the ProcessData active, a write parameters operation is requested, via the command LowMbox [1] = MBOX_PARAM_WRITE), and at the same time it is required a high priority reading:
   

Below there are some tables with an explanation of the public symbols.

To better understand the operation of this unit, we will see how to configure it and use it for a simple management of 2 drives. This type of example demonstrates well the potential of this unit. In fact, after setting up the slave, we're going to set some process data to read and write all the time, we're going to set a table of parameters with which to interface, and we're going to intervene with the use of the mailbox on situations that need a immediate action.

1. Create a new project with QView-6
2. Add a unit type configuration. Edit BUS section according with your product name. In the section INTDEVICE insert the declaration of a device MOSBUS:

   INTDEVICE 
       MdbDevice  MODBUS  0008  1

   Pay attention to the last field number of the declaration (1) that is used to select the communication port. Usually it is 0 for PROG port, 1 for USER port, 2 for aux1, 3 for aux2 port and 43 for ethernet port (modbus tcpip). Check hardware manual for assurance.

3. In the REFERENCES section (always in the unit configuration) add the following code:

   REFERENCES
       MDBMAST1.modbus = MdbDevice

4. Add a unit QCL with a name (for example, MAIN).
5. Add to the project the QCL Feature unit ModbusMaster10 and name MDBMAST1
6. Proceed on the task init of MAIN unit with the protocol setting and slaves setting:

       MDBMAST1.Protocol = MDBMAST1.DEVICE_PROT_RTU    ; modbus rtu
    
       ; setting unit ModbusMaster10 slave table    
       ; node 1
       MDBMAST1.SlaveId[1] 	= 1     
       MDBMAST1.SlaveBitrate[1]    = 9600
       MDBMAST1.SlaveStopBits[1]   = 1
       MDBMAST1.SlaveParity[1]     = 0
       MDBMAST1.SlaveTimeout[1]    = 200
       MDBMAST1.SlaveAddrOffset[1] = 0
       ; node 2
       MDBMAST1.SlaveId[2] 	= 3     
       MDBMAST1.SlaveBitrate[2]    = 57600
       MDBMAST1.SlaveStopBits[2]   = 2
       MDBMAST1.SlaveParity[2]     = 1
       MDBMAST1.SlaveTimeout[2]    = 100
       MDBMAST1.SlaveAddrOffset[2] = 1

   Our network is RTU and consists of 2 drives, one with id 1 and the other with id 3, with different communication settings.

7. Simple process values for the two drives can be the current speed and the set speed. We add these two values also a value of the drive that can identify a working state (stopped, moving, alarm, etc.). Then set the process table:

       ; setting unit ModbusMaster10 process table
       ; read current speed of slave index 1
       MDBMAST1.ProcessId[1]   = 1                      ; slave index (in slave table)
       MDBMAST1.ProcessAddr[1] = &H102B                 ; exadecimal address value
       MDBMAST1.ProcessNum[1]  = 1                      ; number of elements
       MDBMAST1.ProcessType[1] = MDBMAST1.READINREG     ; type of modbus request
       ; write set speed of slave index 1
       MDBMAST1.ProcessId[2]   = 1
       MDBMAST1.ProcessAddr[2] = &H0060
       MDBMAST1.ProcessNum[2]  = 1
       MDBMAST1.ProcessType[2] = MDBMAST1.FORCEREG
       ; read current state of slave index 1
       MDBMAST1.ProcessId[3]   = 1
       MDBMAST1.ProcessAddr[3] = &H00A8
       MDBMAST1.ProcessNum[3]  = 1
       MDBMAST1.ProcessType[3] = MDBMAST1.READINREG
       ; read current speed of slave index 2
       MDBMAST1.ProcessId[4]   = 2
       MDBMAST1.ProcessAddr[4] = &H102B
       MDBMAST1.ProcessNum[4]  = 1
       MDBMAST1.ProcessType[4] = MDBMAST1.READINREG
       ; write set speed of slave index 2
       MDBMAST1.ProcessId[5]   = 2
       MDBMAST1.ProcessAddr[5] = &H0060
       MDBMAST1.ProcessNum[5]  = 1
       MDBMAST1.ProcessType[5] = MDBMAST1.FORCEREG
       ; read current state of slave index 2
       MDBMAST1.ProcessId[6]   = 2
       MDBMAST1.ProcessAddr[6] = &H00A8
       MDBMAST1.ProcessNum[6]  = 1
       MDBMAST1.ProcessType[6] = MDBMAST1.READINREG

8. We also want to use the features of the mailbox to manage a short list of parameters. Then set the param table:

       ; setting unit ModbusMaster10 param table
       ; first parameter of the list (slave index 1)
       MDBMAST1.ParamId[1]      = 1                      ; slave index (in slave table)
       MDBMAST1.ParamAddr[1]    = &H1070                 ; exadecimal address value
       MDBMAST1.ParamNum[1]     = 1                      ; number of elements (maximum 2, to manage double word parameters)
       MDBMAST1.ParamOptions[1] = MDBMAST1.OPTION_MULTI  ; parameter option (use multiple modbus write function)
       ; second parameter of the list (slave index 1)
       MDBMAST1.ParamId[2]      = 1
       MDBMAST1.ParamAddr[2]    = &H1071
       MDBMAST1.ParamNum[2]     = 1
       MDBMAST1.ParamOptions[2] = 0
       ; third parameter of the list (slave index 2)
       MDBMAST1.ParamId[3]      = 2
       MDBMAST1.ParamAddr[3]    = &H1070
       MDBMAST1.ParamNum[3]     = 1
       MDBMAST1.ParamOptions[3] = MDBMAST1.OPTION_MULTI
       ; fourth parameter of the list (slave index 2)
       MDBMAST1.ParamId[4]      = 1
       MDBMAST1.ParamAddr[4]    = &H1071
       MDBMAST1.ParamNum[4]     = 1
       MDBMAST1.ParamOptions[4] = 0

1. After these configuration settings, prepare the feature unit to work:

       ; execute unit command Prepare
       MDBMAST1.Prepare = 1
       WAIT (MDBMAST1.State EQ MDBMAST1.READY) OR (MDBMAST1.State EQ MDBMAST1.ABORTED)
       IF MDBMAST1.State EQ MDBMAST1.ABORTED
           MDBMAST1.Stop = 1                    ; in case of error return to STOPPED state
           ...                                  ; insert the code to notify the error
       ELSE
           MDBMAST1.ProcessEnable = 1           ; process requests can start
       ENDIF

To manage the process values, use the array ProcessValue:

Drive1Vel = MDBMAST1.ProcessValue[MDBMAST1.ProcessOffset[1]]       ; reading current speed
MDBMAST1.ProcessValue[MDBMAST1.ProcessOffset[2]] = Drive1SetVel    ; writing set speed
Drive1State = MDBMAST1.ProcessValue[MDBMAST1.ProcessOffset[3]]     ; reading current state
 
Drive2Vel = MDBMAST1.ProcessValue[MDBMAST1.ProcessOffset[4]]
MDBMAST1.ProcessValue[MDBMAST1.ProcessOffset[5]] = Drive2SetVel
Drive2State = MDBMAST1.ProcessValue[MDBMAST1.ProcessOffset[6]]

ProcessOffset automatically calculates the position of the process element on the array.

In our example, we imagine to use the ParamTable once the drives are fully configured and ready to use. We decide the parameters that we could modify through our application. At this point at least the first time we go to read these parameters, and we have to save them in our retentive area.

The next code example shows how to read all parameters from second drive:

WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_FREE     ; wait until the mailbox is free
MDBMAST1.LowMbox[2] = 2                            ; select slave index 2
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_PARAM_READ     ; read parameters function
WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_REPLY    ; wait until the function ends and replies
IF MDBMAST1.LowMbox[6] EQ 0
    ...                                            ; read parameters successfully (message, change page, etc.)
    slDrive2Par1 = MDBMAST1.ParamValue[3]          ; store the read value on ritentive variable
    slDrive2Par2 = MDBMAST1.ParamValue[4]
ELSE
    ...                                            ; insert the code to menage errors
ENDIF
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_FREE           ; release mailbox

Normally at power, when you enable the connection of a Modbus network drives it is sometimes useful to analyze whether the parameters in the memory are aligned with those on the drives. To do this, we can use the corresponding commands of the mailbox:

MDBMAST1.ParamValue[1] = slDrive1Par1              ; load ritentive value on ParamValue array
MDBMAST1.ParamValue[2] = slDrive1Par2
 
WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_FREE     ; wait until the mailbox is free
MDBMAST1.LowMbox[2] = 1                            ; select slave index
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_PARAM_CHECK    ; check parameters function
WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_REPLY    ; wait until the function ends and replies
IF MDBMAST1.LowMbox[6] EQ 0
    ...                                            ; check parameters successfully (message, change page, etc.)
ELSE
    ...                                            ; insert the code to menage errors
ENDIF
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_FREE           ; release mailbox

You can also use the function MBOX_PARAM_CHECK_ALL to check all parameters of all slaves with a single command.

Finally, we use the write command to set the parameters on the first and on the second drive:

WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_FREE     ; wait until the mailbox is free
 
MDBMAST1.ParamValue[1] = slDrive1Par1              ; load ritentive value on ParamValue array
MDBMAST1.ParamValue[2] = slDrive1Par2
MDBMAST1.ParamValue[3] = slDrive2Par1
MDBMAST1.ParamValue[4] = slDrive2Par2
 
MDBMAST1.LowMbox[2] = 1                            ; select slave index 1
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_PARAM_WRITE    ; write parameters function
WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_REPLY    ; wait until the function ends and replies
IF MDBMAST1.LowMbox[6] EQ 0
    ...                                            ; write parameters successfully (message, change page, etc.)
ELSE
    ...                                            ; insert the code to menage errors
ENDIF
 
MDBMAST1.LowMbox[2] = 2                            ; select slave index 2
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_PARAM_WRITE    ; write parameters function
WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_REPLY    ; wait until the function ends and replies
IF MDBMAST1.LowMbox[6] EQ 0
    ...                                            ; write parameters successfully (message, change page, etc.)
ELSE
    ...                                            ; insert the code to menage errors
ENDIF
 
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_FREE           ; release mailbox

In our example, each unit of a project has the possibility of using single requests for information, to set reference values, or force states of the drives. For these applications we offer 2 mailbox. Why 2 mailbox?

Basically to have two priorities for intervention.

If we use the HighMbox (high priority), we are going to intervene immediately after the current request, which is a read/write process, which is a request to check/read/write parameters, or other demands on LowMbox (low priority) from other units.
This feature was implemented considering the fact that some information must travel as quickly as possible, in our case we can say that in the event of an alarm condition must intervene immediately disabling drives.

Instead, the single requests on LowMbox are used for information that can wait for a while to be completed.

UNIT 1 - low priority request
For example, read some temperatures.

WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_FREE     ; wait until the mailbox is free
MDBMAST1.LowMbox[2] = 1                            ; select slave index
MDBMAST1.LowMbox[3] = &H00A4                       ; address (&H = hexadecimal)
MDBMAST1.LowMbox[4] = MDBMAST1.READREG             ; read holding register modbus function
MDBMAST1.LowMbox[5] = 4                            ; number of elements (read from &H00A4 to &H00A7)
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_SINGLE_REQUEST ; single request function
WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_REPLY    ; wait until the function ends and replies
IF MDBMAST1.LowMbox[6] EQ 0
    temperature[1] = MDBMAST1.LowMbox[7]           ; store the read values on array
    temperature[2] = MDBMAST1.LowMbox[8]
    temperature[3] = MDBMAST1.LowMbox[9]
    temperature[4] = MDBMAST1.LowMbox[10]
ELSE
    ...                                            ; insert the code to menage errors
ENDIF
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_FREE           ; release mailbox

UNIT 2 - high priority request
For example, disable drive for an alarm condition.

IF Alarm
    WAIT MDBMAST1.HighMbox[1] EQ MDBMAST1.MBOX_FREE       ; wait until the mailbox is free
    MDBMAST1.HighMbox[2] = 2                              ; select slave index
    MDBMAST1.HighMbox[3] = &H0009                         ; address (&H = hexadecimal)
    MDBMAST1.HighMbox[4] = MDBMAST1.FORCEREG              ; write holding register modbus function
    MDBMAST1.HighMbox[5] = 1                              ; number of elements
    MDBMAST1.HighMbox[7] = &0474                          ; example value in state register to disable drive    
    MDBMAST1.HighMbox[1] = MDBMAST1.MBOX_SINGLE_REQUEST   ; single request function
    WAIT MDBMAST1.HighMbox[1] EQ MDBMAST1.MBOX_REPLY      ; wait until the function ends and replies
    IF MDBMAST1.HighMbox[6] EQ 0
        NOP                                               ; not operation
    ELSE
        ...                                               ; insert the code to menage errors
    ENDIF
ENDIF

UNIT 3 - low priority request
For example, write a new setpoint on drive.

WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_FREE     ; wait until the mailbox is free
MDBMAST1.LowMbox[2] = 1                            ; select slave index
MDBMAST1.LowMbox[3] = &H88AF                       ; address (&H = hexadecimal)
MDBMAST1.LowMbox[4] = MDBMAST1.FORCEREG            ; write holding register modbus function
MDBMAST1.LowMbox[5] = 1                            ; number of elements
MDBMAST1.LowMbox[7] = 5600                         ; new setpoint value
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_SINGLE_REQUEST ; single request function
WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_REPLY    ; wait until the function ends and replies
IF MDBMAST1.LowMbox[6] EQ 0
    NOP                                            ; not operation
ELSE
    ...                                            ; insert the code to menage errors
ENDIF
MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_FREE           ; release mailbox

• The unit currently handles only Modbus messages type 3 (holding register read), 4 (read input register), 6 (force register) , 16 (force multiple registers). It does not handle modbus messages 1 (read coil) , 5 (force coil), 15 (force multiple coils). These functions are currently selectable, but not yet fully developed.
• It's not possible to configure slaves RTU and TCPIP with the same master. And in that case you need to enter 2 device MODBUS and 2 ModbusMaster10 and divide the network, one for serial slaves and one for tcpip slaves.
• The maximum number of configurable slaves is fixed at 32.
• The maximum number of configurable parameters in Param table is fixed at 200.
• The maximum number of configurable process requests in Process table is fixed at 100.
• The maximum number of configurable process values in ProcessValue array is fixed at 300.
• The maximum number of registers readable or writable with a single message is fixed at 32.
• Mailbox requests relative to parameters, can read/write only one parameter at time (not multiple elements).
• Not all qmove product supports baud rate of 115200 baudrate. Check product documentation.

• For a good use of the unit, it is good to remember to always wait for the mailbox is free before using it, and remember, once you have completed the request, to make it free so that they can be met other requests.

  WAIT MDBMAST1.LowMbox[1] EQ MDBMAST1.MBOX_FREE    ; wait until the mailbox is free
  ...                                               ; request
  MDBMAST1.LowMbox[1] = MDBMAST1.MBOX_FREE          ; at the end release the mailbox

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